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Salt for sale, water for free
"A long-term solution to the city's water problem seems to lie only in desalination of seawater," Tamil Nadu Governor P S Ramamohan Rao said in his Republic Day address, broadcast over AIR and DD.
Chennai faces a host of problems as far as water is concerned: The city is into its fourth year of
drought; its reservoirs are virtually dry; Andhra Pradesh is in no position to help as the level of its own reservoirs in the Krishna-Pennar basin
is
well below the normal; there is growing protests from the small towns/villages around Chennai to tankers drawing water for supply to the city....and desalination is relatively expensive.
When it seemed that there was no way
out comes news that desalination can be inexpensive and that it could be a by-product of the salt industry.
 G
Marimuthu, who holds a doctorate from IIT Bombay, and the executive director of Arun Electro Chemical Systems,
Chennai, says he has developed a new technique which reduces the cost of removing salt from seawater.
There are three methods in vogue for desalination: distillation, reverse osmosis and electrodialysis.
Marimuthu says distillation is possible only if thermal power is available cheaply. Its energy requirement lies between that required for reverse osmosis (RO) and electrodialysis (ED). Nuclear power may be used in the distillation process to make it economical.
However, the plant cost and subsequent maintenance expenses would remain unaffordable.
The reverse osmosis process, which requires minimum energy
among these three methods of desalination, is comparatively economical. However, it suffers from frequent fouling of membranes (which act as salt filters) leading to replacement, which increases the overall cost of the plant.
Electrodialysis is used to desalinate seawater in other parts of the world where cheap electric power is available. For India, conventional electrodialysis is a distant dream. While discussing
desalination, Marimuthu pointed out that he realises the need of the hour to develop an improved design of electrodialysis process to minimise the electric power requirement.
He also pointed out that when he came to Chennai from Mumbai, he saw people running behind lorries for water, which made him decide that he should help Chennaivasis. "We have developed an integrated version of electrodialysis process to include fuel cell-type components. This ensures about 50 per cent of the energy expended on electrodialysis is regenerated. Further reduction in operational cost may be realised if the electrodialysis process produces valuable chemicals besides fresh water."
Explaining his system of electrodialysis, he said the integrated electrodialysis system is basically designed as a chemical reactor to produce valuable chemicals or edible salt from seawater with fresh water as the by-product. Hence, the fresh water is obtained free of cost. The chemical or edible salt produced can be marketed.
The technology produces fresh water free of cost from seawater. In addition, the process generates edible salt or caustic soda, which are saleable. It means that desalination is no longer an expensive technology to get fresh water from seawater.
Around 50 per cent of the power consumption is recovered using hydrogen, which is evolved at one of the electrodes of the electrodialysis system. Based on co-generation or fuel cell principle, hydrogen gas is electrochemically burnt to offset a portion of energy required for the entire process. Energy expended on the plant is partially regenerated this way.
This integrated electrodialysis system becomes highly competitive technology to produce fresh water from seawater. For 1 mld (million litres of water per day), the investment requirement is Rs 10.50 crore. Net profit realised is Rs 1.70 lakh per day if the chemical produced is caustic soda (sodium hydroxide) or Rs 76,000 per day if edible salt is opted for.
 Electron
ion exchange process
Salt has a chemical combination of
Na+Cl- (sodium chloride). When we pass electric current, opposite charged particles attract each other. Negatively charged particles go to the positive electrode and positively charged particles go to the negative
electrode: Na+ goes to the negative electrode and the negative chloride goes
to the positive electrode. The water is now free of salt.
Prototype model and trial results
A prototype model was developed at the company's lab and trials were conducted for generation of fresh water from seawater. The results show a power consumption of only 26.5 KWhr per 1,000 litres of fresh water without co-generation and cost of chemicals produced are taken into calculation. The fresh water produced will have a TDS (total dissolved solids, a unit to measure salt content in the water) of 350 ppm (parts per million), which is within drinking water limits.
Further reduction of TDS is possible with a little extra energy.
The co-generation part would contribute around 50 per cent of the power consumption and the actual power consumption is reduced to 13-14 KWhr. In other words, fresh water is obtained at 5-6 paise per litre. The system design is capable of delivering 20.50 tonnes of caustic soda or 30 tonnes of edible salt per day from a 1 mld plant.
The market prices of these products eventually nullify the cost of production of fresh water and tilt the scale towards profit. The entire plant proposal may be viewed as a lucrative business opportunity by prospective investors.
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we are group of postgratuate..... - neelesh labrath, rajasthan, 9/19/2006
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It is a good technological inn..... - H.H.Madhani, Punen, 1/27/2006
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The technique is good. Is the..... - S.Rameshr, Chennai, 8/18/2004
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Necessity is the mother of all..... - Rohan, Coimbatore, 3/31/2004
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You have not given the phone n..... - K.R.Rangarajan, Not Given, 2/2/2004
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Marimuthu urges the government to adopt this model for desalination, which will be useful
for it in two ways: fulfilling the drinking water needs of the people and producing caustic soda or edible salt.
 Arun Electro Chemical Systems has also developed a model that can be used at home for purification of water, named 'Aqua-4u', which comes with a price tag of
Rs 12,000.
Most of the water from borewells
has high levels of dissolved solids or salt content. Dissolved solids include 'ions' responsible for the ‘salty’ taste and makes the water hard. Iron gives undesirable colour and taste, and arsenic is a potent carcinogenic.
Domestic water purifiers that are available now treat water for suspended solids and microorganisms but fail to resolve the dissolved solids problem. 'Aqua-4U' purifies dissolved solids
in borewell water and gives bacteria-free, pure and safe drinking water.
The cost of purification works out to less than 5 paise per litre, including consumables. Power consumption is 35
w 5 lts/hr. model.
For any further information please contact,
G Marimuthu, Executive Director
Arun Electro Chemical Systems,
Chennai.
Ph: 22532448
N Arun Kumar
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